The food industry uses many naturally derived polysaccharides as stabilizers and thickeners. Other industries use polysaccharides as water treatment chemicals, viscosifiers, thickeners and as surface active materials. Products such as carrageenan, alginate and starch, exhibit unique structural and theological properties such as yield stress and an ability to increase the viscosity in an aqueous environment. The specific structure-function relationships of these biopolymers depend on the individual components such as monomers or repeating units and their chemical linkages.
Polysaccharides which form the bulk of biopolymers in the microbial world have already been noted for their structural importance and are responsible for maintaining the integrity of bacteria and fungi. With the advent of genetic engineering, biosynthesis and manufacture of these biopolymers can be directed to produce molecules with altered physical properties.
Yeast has historically earned its role as an important food grade and industrial organism. The cell wall of Saccharomyces cerevisiae is mainly composed of .beta.-linked glucan. This polymer is responsible for the shape and mechanical strength of the cell walls. The glucan is mainly composed of a backbone chain of .beta.(1-3) linked glucose units with a low degree of inter and intra-molecular branching through .beta.(1-6) linkages. A minor component that consists mainly of a highly branched .beta.(106) linked glucan is closely associated with the main component and both comprise the alkali insoluble glucan fraction.
The following articles deal with the structure of glucans: The Structure of a .beta.-(1-6)-D-Glucan from Yeast Cell Walls by Manners et al., Biochem. J. (1973) 135, 31-36; Evidence for Covalent Linkages between Chitin and .beta.-Glucan in Fungal Wall by Seitsma et al., Journal of General Microbiology (1979), 114, 99-108; Demonstration of a Fibrillar Component in the Cell Wall of the Yeast Saccharomyces cervisiae and its Chemical Nature, by Kopecka et al., The Journal of Cell Biology, Vol. 62 (1974), 66-76; On the Nature and Formation of the Fibrillar Nets Produced by Photoplasts Saccharomyces Cerevisiae in Liquid Media: An electromicroscopic, X-Ray Diffraction and Chemical Study by Kreger et al., Journal of General Microbiology (1975), 92, 202-220; Short Communication Solubility of (13)-.beta.-D-(1-6)-.beta.-D-glucan in Fungal Walls: Important of Presumed Linkage between Glucan and Chitin.
In the prior art processes, aqueous hydroxide extraction of the Yeast Saccharomyces cerevisiae has been practiced, but with a prior step of disrupting the cell walls. This procedure required that the extraction steps be conducted under relatively mild conditions to avoid product degradation. This, in turn, led to the need for multiple extraction steps over a long time period, and therefore is undesirable.